This invention relates to an ostomy appliance, in particular to a filtered pressure relief vent for an ostomy appliance, for example, an ostomy pouch.
The term ostomy includes at least colostomy, ileostomy and urostomy.
Flatus vents have been provided on ostomy pouches to allow flatus gas to escape from the pouch, and hence prevent ballooning of the pouch. However, it is generally desired not to allow all of the gas within the pouch to escape, as this can cause the pouch to collapse against the wearer""s stoma (a problem referred to as pancaking). Such collapsing can be very painful for the wearer, and can also obstruct the passage of faecal matter through the stomal aperture.
It is in practice very difficult to engineer the flow rate characteristics of a filter to achieve adequate flow to prevent ballooning while also avoiding the risk of pancaking. The amount of flatus produced by a person varies widely from one individual to another, and is also dependent on the person""s diet and health.
There have been proposals in the art to fit pressure relief valves to ostomy pouches to regulate automatically the gas pressure within the pouch. Such proposals are described, for example, in U.S. Pat. No. 3,865,109, GB 2094153 and GB 2122499. However, to date, such designs have not found commercial acceptance in ostomy products. It is believed that problems in one or more of the following areas might have made the designs impractical for large scale production: reliability; reproducibility; difficulty of manufacture; size; and cost.
Therefore, there remains a significant need for an automatic pressure relief vent which overcomes the problems of the prior art.
Broadly speaking, one aspect of the present invention is to provide a pressure relief valve for an ostomy pouch, the valve having one or more of the following characteristics:
(a) The valve includes a movable diaphragm, at least one of the diaphragm and its seal seat comprising or carrying a sticky and/or tacky and/or oily and/or greasy material. Such a feature can ensure that a reliable seal is formed between the diaphragm and the seal seat to prevent unwanted leakage at low pressures, without requiring a strong bias to hold the diaphragm against the seal seat.
(b) The valve includes a movable diaphragm (or diaphragm) which is pinched or held at, or towards, a first edge region of the diaphragm, leaving a generally opposite second region of the diaphragm unhindered. The diaphragm functions as a flap. Such a feature can enable the size of the valve to be reduced, compared to more conventional rotationally symmetric proposals known in the prior art.
The resistance offered by the flap will be affected by characteristics including the stiffness of the diaphragm material, the size and thickness of the diaphragm, and the position and size of the means for gripping or pinching the fixed region of the diaphragm. These factors can be engineered to achieve suitable pressure responsive characteristics. For example, for a given size of diaphragm, and a given diaphragm material, it is still possible to control the pressure at which the diaphragm opens by selecting an appropriate fixed grip position of the diaphragm about which the diaphragm has to bend to open.
(c) The valve includes a deformable (preferably bendable) diaphragm (or diaphragm) having a thickness/lateral dimension ratio of not significantly less than about 1/30  (i.e. not significantly less than 0.03). Preferably, the ratio is larger and, with increasing preference for larger ratios, is at least about 1/20, 1/15, 1/12, 1/10, 1/9, 1/8  and most preferably at least 1/7. If the diaphragm has more than one lateral dimension (e.g. if not circular), then the above ratio should apply to at least the smallest lateral dimension. Such a feature may enable more consistent characteristics to be achieved, and is in contrast to relatively thin bendable diaphragms suggested in the prior art.
(d) The pressure at which the valve opens is less than about 0.15 psig, and preferably is less than about 0.1 psig. (The term psig refers to psi xe2x80x9cgaugexe2x80x9d, and indicates a positive pressure differential across the valve, i.e. a positive pressure inside the pouch relative to external atmospheric pressure outside the pouch).
(e) The valve diaphragm is protected from direct contact with liquid and/or solid stomal discharge, by means of a protection layer which is of a material, or is so arranged, to act as a barrier (or obstacle) to liquid, while permitting the flow of gas. For example, the protection layer may consist of microporous PTFE.
(f) The valve unit comprises a diaphragm which precedes the or a filter material.
(g) The valve includes a filter which selectively blocks the passage of certain gases (including selected unpleasant odorous gases) such that those gases remain trapped within the pouch. Such a feature is in contrast to many conventional ostomy filters which adsorb the unpleasant gas molecules within the filter.
(h) The valve comprises a casing containing a movable diaphragm (or diaphragm), the case comprising a first part securable to the pouch and defining a well for receiving the diaphragm, and a second part receivable within the well to cover the diaphragm. Preferably, the second part is dimensioned to be received substantially entirely within the well. Preferably, the second part is secured to the first part by a mechanical interlock. Preferably, the second part comprises an outlet aperture for allowing gas escaping past the diaphragm to exit from the casing.
(i) The valve is or comprises a so-called coffee-bag-type vent. Such vents are known in the very different field of coffee packaging, to allow excess pressure to be relieved from packets of coffee. Designers in that field are faced with different technical problems from those discussed above. In particular, one problem is how to preserve the pleasant aroma of the coffee, in contrast to the problem in the ostomy field of how to quash unpleasant odours to which the human nose is highly sensitive. To the best of the inventor""s knowledge, it is not known hitherto to use such a valve in the ostomy field.
An example of a so-called coffee-bag-type vent is described in EP-A-0659657.
In a second aspect, the invention provides an envelope (or sub-envelope) for use in an ostomy pouch, the sub-envelope having first and second apertures, a deodorising filter communicating with the first aperture and a pressure relief valve communicating with the second aperture, the envelope defining a buffer chamber for gas between the deodorising filter and the pressure relief valve.
Preferably, the envelope is inflatable at least to some extent.
Preferably, the deodorising filter is secured to the envelope wall in a region around the first aperture.
Preferably, the pressure relief valve is secured to the envelope wall in a region around the second aperture.
The first aperture may be an inlet aperture for gas entering the sub-envelope, and the second aperture may be an exit aperture for venting gas externally. Alternatively, the functions of the apertures may be swapped.
Preferably, the pressure relief valve is of a type which opens automatically when a desired threshold pressure is reached.
In a third aspect, the invention provides an ostomy pouch comprising a pressure relief valve and a deodorising filter, the deodorising filter being offset from the pressure relief valve.
Preferably, the deodorising filter does not overlap the pressure relief valve. This can allow the filter element and the pressure relief valve to be mounted in a minimum profile height, to avoid increasing the thickness of the ostomy pouch unnecessarily.
Preferably, the deodorising filter is spaced from the pressure relief valve.
Preferably, the deodorising filter and the pressure relief valve are mounted on a sub-envelope within the pouch. Preferably, the sub-envelope defines a buffer chamber for gas between the deodorising filter and the pressure relief valve.
In a further aspect, the invention provides an ostomy appliance comprising any of the aforesaid arrangements. Preferably, the appliance is an ostomy pouch.